1. Field of the Invention
This invention relates to electronic circuits, and more particularly, to an efficient method of input/output (I/O) port overvoltage protection of a high-speed port.
2. Description of the Relevant Art
A Universal Serial Bus (USB) is a standard serial bus interface for connecting devices, such as multiple computer peripherals or portable music and video players, to a host computer for easy transfer of data by means of hot swapping, or allowing devices to be connected and disconnected without a need to reboot the computer or to turn off the device. This means of connecting is also referred to as hot plugging. USB allows several devices to be used without requiring manufacturer-specific device drivers to be installed on the host computer. The USB Implementers Forum (USB-IF), an industry trade association incorporating companies from the computer and electronics industries, standardizes the design of USB. USB is intended to replace many legacy varieties of serial and parallel ports, and for many computer peripherals, USB has become the standard connection protocol.
A USB interface is a master/slave architecture. From the frame of reference of a USB interface, the master is referred to as the “upstream” device, or host/hub, and the slave as the “downstream” device. The interface consists of four wires: D+, D−, VBUS, and Ground. The two data lines, D+ and D−, are for bi-directional data transfer and use differential drive techniques. The wires VBUS and Ground are used to distribute power from the upstream host to the downstream device. Again, the terms “upstream” and “downstream” are from the point-of-view of a particular USB interface.
USB devices are linked in series through hubs. A USB hub is a device that allows many USB devices to be connected to a single USB port on the host computer or another hub. Each hub has one upstream port and a number of downstream ports. The upstream port connects the hub (directly or through other hubs) to the host. Other hubs or devices may be attached to the downstream ports. USB hubs may be built into equipment, such as computer keyboards, computer monitors, a personal computer (PC), a smartphone, a video game console, an automotive infotainment system comprising one or more of a navigation application with real-time traffic, a hands-free communication application, and an audio/video storage and playback application; or other. Automobile manufacturers have begun to include USB ports in vehicles, such as in dashboards or center consoles, that permit the connection of USB peripheral devices to the in-vehicle entertainment system, or infotainment system. Now, a portable audio player may be allowed to play audio and to control and display functions using the vehicle's own system. Ford Motor Company's SYNC system is one example.
A system with inherent higher voltages than USB levels, such as an automotive infotainment system, introduces design issues not previously considered in industry specifications, such as the USB 2.0 Specification from the USB Implementers Forum. The original applications for USB hubs were intended primarily for connecting digital devices, or USB peripheral devices, both together and to host computers while operating at a low voltage. The maximum allowable voltage levels on the data and power lines of USB interfaces are less than the voltage levels used on lines both within automotive electronic modules and on wiring external to automotive electronic modules. For example, the USB data and power lines are typically powered up to 5V, and an automotive battery is able to supply 12V. USB lines within an automotive dashboard or center console may be destroyed in the event they are shorted to the positive potential of a 12V automotive battery. Many manufacturers of electrical automobile systems refer to the International Organization for Standardization (ISO) 7637 for defining electrical transient protection, which allows higher voltages than typical USB voltage levels.
In addition to no industry specifications addressing overvoltage protection of USB lines within systems coupled to much higher operating voltages, designs of a proposed overvoltage solution must meet several requirements. Some examples of these requirements include quick response to electrical surges and transients to maximize protection, low capacitance to minimize signal attenuation, small packages to minimize footprint for space-constrained modules, support high-speed data rate, and satisfy a USB-IF eye pattern diagram.
USB IF eye pattern diagrams may be used to diagnose signal-integrity problems that corrupt serial data in digital-communication systems. Test Points 2 and 3 of the USB 2.0 Specification addresses new manners by which generation of eye pattern diagrams for packetized data are performed. The USB 2.0 Specification describes difficult requirements to meet for overvoltage protection devices such as the rise and fall times, signal levels, and pulse skew of a corresponding eye pattern diagram. Even further, overvoltage protection of the data lines may be more difficult due to the high-speed data rate support of 480 MBits/sec for these data lines. At this speed the capacitance and inductance of the circuit board, connectors, and any additional circuitry becomes critical. These high-frequency capacitive and inductance effects make it difficult to satisfy all of the above requirements.
In view of the above, efficient methods and systems for input/output (I/O) port overvoltage protection of a peripheral device are desired.